1. Field of the Invention
This invention relates generally to the production of furan and, more particularly, to a novel process for converting furfural aldehydes to furan. Specifically, the process of the present invention relates to an improved process for converting furfural corresponding derivatives, which furfural aldehyde and its derivatives are in turn byproducts of the conversion of biomass materials to methanol, gasoline and other fuels.
2. Description of the Prior Art
The conversion of renewable resources, such as biomass and organic wastes, to conventional liquid and gaseous fuels has been approached from several perspectives. One approach includes the fermentation of sugars to ethanol, although this process leaves the lignin and usually the hemicelluloses as byproducts. Another approach includes the complete gasification of biomass to a syngas containing carbon monoxide and hydrogen, followed by the catalytic conversion to alcohol and/or hydrocarbons. While the process is technically feasible, it requires high vapor pressures. Other procedures include pyrolysis and acid hydrolysis of various solid biomass materials to liquid and gaseous fuels.
One of the byproducts of such processes in the wood-to-ethanol conversion as well as other related biomass conversions is the production of furfural aldehydes and derivatives thereof. In order to maximize the economics of such processes, it is highly desirable to be able to convert such byproducts to useful materials.
Furfural aldehyde and its derivatives so produced from biomass conversion have generally had limited uses in the past. However, one potentially important use is in the production of furan and its various derivatives, which in turn have significant potential as octane enhancers and boosters in various gasoline blends. In particular, methylated furans have particularly high blending octane numbers making them especially useful and ecoomic products. In general, the conversion of furfural aldehyde and its derivatives to furan and its counterpart derivatives has been achieved utilizing a variety of existing commercial processes. These processes include a variety of catalytic techniques which, unfortunately, have several drawbacks. In particular, these techniques generally utilize a transition or noble metal catalyst which either produces low yields of furan and furan derivatives or is highly expensive to use due to either the high costs of obtaining the catalyst or of rejuvenating the catalyst for reuse.
A more recent catalytic development for the conversion of furfural aldehyde to furan includes the use of a palladium catalyst on a basic support such as barium sulfate or alumina. This particular process, which is disclosed in U.S. Pat. No. 3,223,714, also requires the use of a dry furfural as a feedstock. This aspect requires an extra purification step and therefore increases the costs associated with this conversion technique. It should be noted that one of the embodiments of this patent includes the use of palladium on a silica-alumina catalyst base, although the actual catalyst itself is the palladium while the silica-alumina functions merely as a structural support. However, when the palladium on such a base is utilized in an acid environment, the catalyst is found to have no activity.
The use of a silica-alumina, or zeolite, catalyst has become very widespread for many different process applications. In particular, the use of a medium pore size zeolite, ZSM-5, has been studied with a wide variety of feedstocks. Typically, however, ZSM-5 is well-known to be an acidic catalyst and therefore highly inappropriate for selective deoxygenation to decarbonylate furfural aldehydes while retaining the ring oxygen. A paper entitled, "Conversion of Biomass Carbohydrates into Hydrocarbon Products" by H. Hanniff, et al., was presented at the IGT/CBETS Conference on "Energy from Biomass and Wastes X" in Washington, D.C., Apr. 7-10, 1986. This paper disclosed, among other items, that furfural can be converted to furan using an HZSM-5 catalyst and resulted in a conversion efficiency of up to 50%. However, higher conversion efficiencies were not reported. Moreover, when the authors co-fed methanol with the furfural, very low yeilds of oxygenated compounds were produced, and neither methyl furan nor any other form of methylated furan was produced. In fact, this particular disclosure teaches that methanol, when added to furfural aldehyde, aids in the destruction of the furan moiety. Thus, there remains a need for an efficient and economic catalytic process for high-efficiency conversion of furfural aldehydes to furans and in particular methylated furans in conjunction with the overall process for converting biomass materials to liquid and gaseous fuel products.